1. Field of the Invention
The present invention relates to an ink jet ink which has high environmental gas resistance and provides good images in which the occurrence of metallic luster, the so-called bronze phenomenon, is suppressed even when the ink is printed on a recording medium. The present invention also relates to an ink set, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus each using the ink jet ink.
2. Related Background Art
An ink jet recording method is a recording method of applying a small ink droplet to any one of recording media such as plain paper and glossy media to form an image, and has become rapidly widespread owing to reduction in costs and improvement in recording rate. With the rapid spread of digital cameras in addition to improvement in the quality of images recorded by the method, the method has been generally used as a method of outputting photographic images comparable to silver halide photograph.
In recent years, image quality has undergone improvement more than ever owing to, for example, extreme reduction in size of an ink droplet and an improvement of the color gamut involved in the introduction of multi-color ink. Meanwhile, there have been growing demands for coloring materials and inks, and stricter properties have been required in respect of improvement of color developability and reliability concerning anti-clogging or ejection stability.
As compared with the silver halide photograph, the ink jet recording method is problematic in respect of, for example, the image storage stability of the resultant recorded product. In general, the recorded product obtained by the ink jet recording method is inferior in image storage stability to that by the silver halide photograph, and involves the emergence of a problem in that a coloring material on the recorded product is apt to deteriorate to cause a change in the color tone of the image and the color fading of the image when the recorded product is exposed to light, heat, environmental gases present in the air, or the like for a long period of time. In particular, the enhancement of environmental gas resistance to the level of silver halide photograph has been of a concern from the past in the ink jet recording method. Cyan has the lowest environmental gas resistance among yellow, magenta, and cyan, which are hues used for ink jet ink. Therefore, the enhancement of the environmental gas resistance of cyan ink to the level comparable to that of yellow ink or magenta ink is of one important concern in the ink jet recording method.
The basic skeletons of coloring materials for ink jet ink having a cyan hue are roughly classified into a phthalocyanine skeleton and a triphenylmethane skeleton. Representative coloring materials of the former include C.I. Direct Blue 86 and 87, and C.I. Direct Blue 199. Representative coloring materials of the latter include C.I. Acid Blue 9.
In general, a phthalocyanine-based coloring material is characterized in that it is excellent in light resistance as compared with a triphenylmethane-based coloring material. Furthermore, the phthalocyanine-based coloring material has high fastness properties against humidity or heat and has good color developability, and so the coloring material has been widely used as a coloring material for ink jet ink.
However, the phthalocyanine-based coloring material tends to be poor in fastness against environmental gases in the air (such as ozone, Nox, or SO2), especially an ozone gas. In particular, in a recorded product obtained by applying the coloring material on a recording medium having an ink-receiving layer containing an inorganic substance such as alumina or silica, the fastness is significantly low, hence the color fading of the recorded product is remarkable when the recorded product is left standing in a room for a long period of time. Various compounds to be added to ink have been disclosed for the purpose of improving the environmental gas resistance (see, for example, Japanese Patent Application Laid-Open No. H05-171085, Japanese Patent Application Laid-Open No. H11-29729, Japanese Patent Application Laid-Open No. H10-130517, Japanese Patent Application Laid-Open No. 2000-303009, and Japanese Patent Application Laid-Open No. 2002-249677). However, none of those publications has achieved compatibility between good color developability and high environmental gas resistance for ink jet ink.
The phthalocyanine-based coloring material involves another problem, that is, the occurrence of metallic luster resulting from the high aggregation properties of the coloring material, the so-called bronze phenomenon. When the bronze phenomenon occurs in a recorded product, the optical reflection properties of the recorded product change. As a result, the color developability and hue of an image remarkably change, with the result that the image quality is significantly lowered. The bronze phenomenon is considered to occur as a result of the aggregation of the coloring material on the surface of a recording medium due to, for example, the high aggregation properties of the coloring material in ink and a lowering in permeability of the ink into the recording medium when the ink is applied to the recording medium. In particular, a coloring material with an amino group introduced in its molecule for the purpose of improving environmental gas resistance, or an ink containing a coloring material having low solubility in water tends to significantly cause the bronze phenomenon.
For example, it has been proposed that a specific phthalocyanine-based coloring material is used to improve the environmental gas resistance (see, for example, Japanese Patent No. 2942319). The use of the specific phthalocyanine-based coloring material provides the environmental gas resistance which is of one concern in the phthalocyanine-based coloring material. However, in the proposition, there is no reference to the bronze phenomenon, and hence, resistance to the bronze phenomenon of the coloring material is unclear. In other words, the compatibility between resistance to bronze phenomenon (bronze resistance) and environmental gas resistance has not yet been achieved.
Therefore, it is indispensable to conduct research on ink jet ink using a phthalocyanine-based coloring material which is excellent in color developability, has high environmental gas resistance, and suppresses the occurrence of the bronze phenomenon.